1. Field of the Invention
The present invention generally relates to an ATM (asynchronous transfer mode) switching system. More specifically, the present invention is directed to an ATM switching system capable of equally distributing calls so as to avoid call concentration.
2. Description of the Related Art
In an ATM switching system, when an incoming call (receiving) request is issued from a network, an incoming call receiving control is carried out so as to call a call receiving terminal only in the case that such a resource for satisfying a call reception request condition issued from this network can be secured. The call reception request condition contains, for instance, a band required to a call, and an identifier (ID) of a call receiving user.
The more the call receiving terminal which is requested to receive the call from the network is brought into busy condition, the larger the call loss rate would be increased. As a consequence, such a call loss rate lowering problem is solved by constituting a single group by employing a plurality of call receiving terminals, and further by executing the call receiving control to this single group in accordance with the below-mentioned method.
That is, in accordance with this method, when the incoming call request is issued to a representative call receiving terminal, a detection is made in the register sequence as to whether or not the call receiving terminal registered into this group is under busy state. Then, when such a call receiving terminal not under busy state is firstly detected, the incoming call receiving control is performed to this call receiving terminal. In other words, the incoming calls are distributed.
It should be understood that a "call loss rate" implies such a probability that since a counter party (call receiving destination) is under busy state, a call connection is refused.
On the other hand, in the above-described conventional incoming call control method, there is another problem that the incoming calls would be readily concentrated onto the incoming call receiving terminal the register sequence of which is low, and therefore, these incoming calls may not be equally distributed to other incoming call receiving terminals within the group.
To solve this problem, the quantity of incoming calls is counted with respect to each of the incoming call receiving terminals, and then these incoming calls are distributed in such a manner that the number of incoming calls for the respective terminals are equal to each other in the above-explained conventional incoming call control method.
However, even this solving manner would cause the below-mentioned problem. That is, there are incoming calls having short communication time, and incoming calls having long communication time. As a result, when the incoming call having a short or a long communication time is merely counted as one irrelevant to the actual communication time, there is such a problem that the incoming calls would be concentrated onto the incoming call terminal to which the call having long communication time has been distributed.
As a consequence, the Applicants could conclude that the above-described problem would be caused by such a condition that the incoming calls are not distributed while communication amounts become equal.